Method of sweetening sulphurous petroleums



Patented Jan. 13, 1931 UNITED STA ES PATENT OFFICE HUGH HARLEY CANNON AND WEIGHT W. GARY, 01'! LOS ANGELES, CALIFORNIA,

assrenons, BY mEsNE ASSIGNMENTS,

TO CANNON-PRUTZMAN TREATING PROC- ESSES, LTD, 01'' LOS ANGELES, CALIFORNIA, A CORPORATION OF CALIFORNIA METHOD OF SWEETENING SULPHUBOUS IPETROLEUMS No Drawing.

An object of our invention is to provide a reagent and a method for converting the mercaptans or alkyl hydrosulfids which occur in petroleum distillates into the corresponding alkyl disulfids.

A further object of our invention is to provide such a reagent which is .at once cheaper and more effective than the reagents heretofore used for this purpose.

A further objectof our invention is to provide a reagent which is suited for apphcation to the oil in the form of a substantially dry powder.

The hydrosulfids or mercaptans, having the general formula RSH, are found in the distillates from almost all sulfur containing petroleums. The members of this group are chemically unstable, actively attack copper and brass and have a most objectionable odor. They are therefore highly undesirable constituents of commercial gasoline.

The well known process of sweetening consists in converting the mercaptans into the corresponding disulfids, bodies which are stable, noncorrosive and of a mlldodor. As ordinarily practiced this converslon s effected in two steps. In the first the 011 is treated with an aqueous solution of lead oxid (lithar e) in caustic soda, this solution containing t e hypothetical sodium plumbite, a body whichhas not hitherto been prepared in the dry form. By thls solution the mercaptans are converted into lead salts, the so-called lead mercaptids which separate only slowly and incompletely from the oil. In the second step the lead salts are decomposed by the addition of free sufur, the lead being precipitated as a sulfid while the two alkyl-sulfur radicles previously attached to the lead conjoin to form the dialkyl-disulfid.

The reactions which are believed to take place are as follows:

All the sulfur originally present in the mercaptan is also found in the disulfid and the process is therefore not one of desul- Application. filed January 21, 1929. Serial No. 884,004.

furization but is merely the conversion of a compound having deleterious properties into one which is relatively innocuous. be understood that the above remarks apply to the prior art.

We have discovered that a lead salt'of any of the alkali earth metals, and particularly alead salt of calcium, may be prepared in a form suitable for use in the above described sweetenin process, that these salts have mani old advantages over the sodium salt heretofore used. The earth metal salts are much cheaper than the sodium salt; they are very readily prepared; they are not caustic in handling and do not corrode metals nor cree nor absorb carbon dioxid, and they may prepared in the form of dry powders and are fully effective in such form. Because of this property they may be filtered out of the treated oil, reducing sludge losses to a minimum.

Other comparisons are: that the sodium salt has a powerful action on the oil other than the desired converting action, forming water-soluble salts with phenols, naphthenic acids and unsaturated hydrocarbons, these salts rapidly accumulating in the solution if an attempt is made to use it repeatedly. The alkali earth metal salts are inert in this respect and do not load up with organic matter if reused. The sodium salt promotes the formation of undesirable and dark colored gums in sour, unstable oils, while the earth metal salts do not. The sodium-salt when repeatedly used, has been found to have a strong tendency toward oxidation to sodium sulfate in the presence of lead sulfid and air, while the earthfmetal salts have no such tendency. Finally, the spent earth metal reagent may be regenerated and brought back to its original efliciency by a simple and cheap manipulation.

We prepare our new reagent in the following manner, using lime (calcium hydroxid) as an example of any alkali earth hydroxid. With any desired quantity of commercial litharge we admix a suitable proportion of commercial hydrated .lime and, after thorough blending, add sufficient and water to produce a thick pasteor' cream. From this the excess water may be removed b filtering. The water required to produce tile reaction is only that required to dampen the mass and, if preferred, only this quantity may be added, thus avoiding the filtration. The water, however, must be completely disseminated throughout the mass, a somewhat diflicult matter unless some sort of pugging apparatus is: available.

The damp mass is then dried in an convenient manner to such consistency t at it may be finely pulverized. It may contain fifteen percent by weight of water or even more, or it may be rendered completely dry, without any appreciable effect on its activity as a reagent, and it may be dried at any temperature up to at least 300 F. and prob ably at even higher temperatures.

The preferred proportion of alkali earth metal hydroxid to lead oxid for the above mixture is indicated by the following relations:

CaiOH) :PbO:: 74:223 Ba OH) :PbO::172: 223 Sr(QH) :PbO::122:223

As the lead oxid is the more expensive of the two constituents it is desirable to use a small excess of the hydroxid, up to say ten percent over the calculated quantity (though even-a much greater excess is entirely harmless), and the water contents as S :Pb::64:207.,

An excess of not less than ten percent over the calculated quantity of lead should be allowed to ensure completion of the conversion. If the quantity of mercaptan sulfur is not known the oil should be dosed with small quantities of the reagent until it indicates sweet to the well known doctor test. An excess of reagent is harmless exce t as it is wasteful.

he spent reagent may now be settled and withdrawn as a sludge or the next step ma be carried out without removing it. ThlS step consists in cautiously adding finely, pulverized free sulfur until all the lead is precipitated as lead sulfid. Even a slight excess of sulfur will render the oil corrosive to metals and should be avoided. If the quantity of mercaptan sulfur is known the dose of free sulfur to .be added will be just one half the mercaptan sulfur as will be evident from the reactions below. If this quantity is not knownthe free sulfur should be added in small doses with constant agitation until a sample of the oil, filtered to remove sediment, shows no black or brownish discoloration when treated with a inch of free sulfur. e are uncertain as to whether it is more desirable to proceed to the second step without removal of the excess of reagent or after its removal. It is simpler operation to leave it sus ended in the oil and to proceed at once to t e precipitation with sulfur. On the other hand it appears that when this rocedure is followed there is some reaction etween the sulfur and the necessary remainder of unused chemical, causing a loss of both reagent and sulfur and maklng the determination-of the end point for sulfur addition somewhat uncertain, with danger of over-addition and the consequent production of a corrosive oil. Apparently a slight gain in economy and certainty must be balanced against an added convenience, with no material advantage on either side.

The reactions occurring in the preparation of the reagent and in the treatment of the oil we believe to be as follows, though we would not be understood as limiting ourselves thereto:

As a final step the spent reagents, which will be found as a dry powder suspended in the oil, may be allowed to settle and the clear oil decanted, or preferably the oil may be filtered through cloth and the sediment thus removed completely. If the above instructions have been followed the most refractory oil will now be found to be completely sweetened, the mercaptans being en- .tirely converted into the corresponding It will be understood that the sweetening result produced in the manner above described will not be obtained if the two constituents of the reagent mixture be separately ap lied to the oil, as neither the alkali meta hydroxid nor the lead monoxid has any'material sweetening effect. The sweetening effect is due to the joint action of the two agents and is probably due to the formation of a compound, as for instance the hypothetical calcium plumbite, between the lime and the lead. So far as we know the existence of this or of any definite compound cannot be positively proven, and in the appended claims we .lay claim to the in- We claim as our invention: I

1 The method of converting mercaptans into lead mercaptids, comprismg: treatin a liquid-containing said mercaptans wit 5 a powdered solid comprising lead monoxid and a hydroxid of an alkali earth metal.

2. The method of converting mercaptans into lead mercaptids, comprising: treating a liquid containing said mercaptans with a powdered solid com rising lead monoxid and calcium hydroxi 3. The method of sweetening oils containing mercaptans, comprising: treating said oils with a powdered solid comprisin an alkali earth metal hydroxid and lea monoxid to convert the mercaptans into lead mercaptids and thereafter precipitating the lead from said mercaptids.

4. The method of sweetening oils containing mercaptans, comprising: treating said oils with a powdered solid comprising an alkali earth metal hydroxid and lead monoxid to convert the merca'ptans into lead mercaptids and thereafter preci itating the lead from said mercaptids by t e addition of sulfurto said oil.

5. The methodof sweetening oils containing mercaptans, comprising: treating said oils with a powdered solid comprising calcium hydroxid and lead monoxid, to convert the mercaptans into lead mercaptids and thereafter precipitating the lead from said mercaptids by the addition of sulfur to said oil. a

6. The method of sweetening oils containing mercaptans, comprising: treating said oils with a powdered solid comprising calcium hydroxid and lead monoxid, to convert the mercaptans into lead merca tids and thereafter precipitating the lead rom said mercaptids.

In witness that we claim the foregoing we have hereunto subscribed our names this 31st day of December, 1928. 

